1. Field of the Invention
The invention relates to a projecting device, and more specifically, to a projecting device with a cylindrical color tube for displaying color images.
2. Description of the Prior Art
Commonly, images are displayed by a projecting device by projection onto a screen. The projecting device can display images of various colors.
Please refer to FIGS. 1 to 3. FIG. 1 is a perspective view of a prior art projecting device 10. FIG. 2 is a schematic diagram of the projecting device 10. FIG. 3 is a front view of the color wheel 18 in FIG. 2.
The projecting device 10 comprises a housing 12, a light source 14 installed in the housing 12 for generating a trichrome light beam 16, a color wheel 18 rotatably installed in the housing 12 having red, green and blue dichroic filters 20, 22, 24 installed on a surface of the color wheel 18 for filtering the trichrome light beam 16 into red, green and blue light beams 26, an electric motor 28 installed in the housing 12 for rotating the color wheel 18 so as to generate the red, green and blue light beams 26 one by one, a digital micro-mirror device (DMD) 30 installed in the housing 12 for converting an image signal into an image and modulating the image into each of the red, green and blue light beams 26 outputted from the color wheel 18 to generate a modulated light beam 32, and a projecting lens 34 installed in the housing 12 for projecting the modulated light beam 32 onto a screen 36.
The color wheel 18 can filter the trichrome light beam 16 into the red, green and blue light beams 26 one by one. However, the red, green and blue dichroic filters 20, 22, 24 each occupy a sector-shaped portion of the color wheel 18. Therefore, when filtering the light beam 16, it cannot pass through the center of the color wheel 18. Thus the color wheel 18 has to be made very large, increasing the size of the projecting device 10. The projecting device 10 is quite unmarketable because of its large size.
It is therefore a primary objective of the present invention to provide a projecting device to solve the above mentioned problem.
Briefly, in a preferred embodiment, the present invention provides a projecting device comprising a cylindrical color tube for filtering a trichrome light beam transmitted from a light source. The color tube has red, green and blue dichroic filters installed along its cylindrical side. When the trichrome light beam is transmitted through the color tube, it will be filtered into red, green and blue light beams. The red, green and blue light beams will be modulated to generate a modulated light beam. And the modulated light beam will be projected onto a screen.
It is an advantage of the present invention that the color tube has a very small size, reducing the size of the projecting device. This allows the projecting device to be quite marketable because of its small size.